In many applications, composite sandwich panels are partially or entirely curved, rather than having only planar surfaces. A prominent example is the blades of wind turbines used to produce electrical energy. These blades are commonly comprised of sandwich panels, and the cores of those panels are required to conform to specified curvatures within the blades. The principal core materials used today in the production of wind turbine blades are balsa wood and foam plastics. In prior art, conformability of these materials is often achieved by cutting or scoring through the thickness of the wood or foam core to divide it into a plurality of strips or blocks of rectangular cross-section. These are adhesively connected, on only one face of the core, to a continuous flexible sheet material, commonly a scrim comprising fiberglass rovings.
The flexible scrim serves as articulated joints between each of the rigid strips or blocks. When the core panel embodying prior art is placed into a concave mold, with the non-scrim face of the panel against the mold surface, the strips or blocks hinge open relative to one other, forming wedge-shaped spaces within the core panel between opposing surfaces of the strips or blocks. These spaces fill with resin during the molding process, thus increasing the weight and cost of the sandwich panel. The resin within the spaces is not combined with reinforcing material, such as fiberglass, so its structural contribution to the panel is severely limited.
In some core panels, the low density cellular material is scored mostly, but not entirely, through the thickness of the core, and the flexible sheet material is omitted. The cutting or scoring of the balsa wood or foam plastic is generally done using saw blades, and the score lines comprise saw kerf voids which fill with undesired molding resin even when the core panel is in a planar position in a non-curved mold. The saw kerfs between the strips or blocks permit a limited degree of articulation when the core panel is placed in a concave mold with the scrim against the mold surface, but the core panel retains wedge-shaped voids between the strips or blocks which fill with excess resin.